Electric discharge apparatus



June 21, 1960 w. E. LARGE 2,942,151

ELECTRIC DISCHARGE APPARATUS Filed Aug. 16, 1957 WITNESSES #NVENTOR g3 William E. Large United States Patent "ice ELECTRIC DISCHARGE APPARATUS William E. Large, Clarence, N. assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a cor- I poration of Pennsylvania Filed Aug. 16, 1957, Ser. No. 680,901

'14 Claims. (Cl. 315-203)v ducting. V

Fail-safe timers constructed in accordance with the teachings of the prior art have been found to be incapable of reliably timing an interval of relatively long duration for example of the order of a few seconds. In addition, such prior art timers have been found not to be positive in signalling the end of the timed interval. They have a tendency to phase off; that is, the current which flows during the timed interval instead of falling abruptly to zero at the end of the interval gradually drifts to zero magnitude. i

It is accordingly an object of this invention to provide a fail-safe timer capable of timing an'interval of long duration.

Another object of this invention, is to provide a failsafe timer which shall not phase ofi but shall positively signal the end of the timed interval.

In accordance with this invention, a timer is provided which includes an electric discharge device preferably of the gaseous type having a pair of control electrodes.

The-discharge device is controlled from a time constant network preferably including a capacitor and discharging impedance which may beset to time the discharge of the capacitor. During standby the capacitor is disconnected from the discharge device andthe discharging impedance and is charged. To maintain the discharge device non-conducting during standby a biasing potential is impressed between the one control electrode audthe cathode. During operating the capacitor is connected to the'other control electrodes of the discharge device and to the impedance so that it is discharged through the impedance and the path between the latter control electrode and the cathode. The connection is such that the dis-' charge device is maintained conducting so long as the network is discharging. The capacitor discharge circuit includes an alternating current supply which at the end of the discharging interval reverses the charge on the capacitor. By the cooperation of the charge reversal on the capacitor and the bias potential positive timing of long intervals is improved. I

The novel features considered characteristic of this invention are described generally above. :The invention v itself both as to its organization and as to its method of operation together with additional advantages and objects thereof, will be understood from the following description of; a preferred embodiment taken in connection with the 1 accompanying drawinginwhich:

Patented June 21, 1960 Fig. 1 is a circuit diagram of a preferred embodiment of this invention;

Fig. 2 is a diagram similar to Fig. 1 but showing the magnitudes of the components of apparatus which has been constructed and found to operate satisfactorily.

Fig. 2 is presented only for the purpose of aiding those skilled in the art in practicing this invention and not with any intention or in any way limiting the scope of this invention.

The apparatus shown in the drawing includes an electric discharge device 1TU preferably a thyratron having an anode 11, a cathode 13, a first control electrode 15 and a second control electrode 17. This apparatus is supplied from a transformer 1T the primary lP of which may be connected to a commercial alternating-current supply through the usual disconnects or circuit breakers (not shown). Anode potential for the discharge device 1TU is supplied from one secondary 181 and potential for heating the cathode 13 is derivable from another secondary 182 of transformer IT. The dots at the ends of the secondaries 181 and 182 identify the terminals of the secondaries which are simultaneously at the same plurality. I

One terminal of the secondary 181 is connected to the anode 11 through the coil of a relay 2CR which symbolizes a load. The coil is shunted by a resistor 19. The relay 20R has a normally open contact 20 which is connected to the system (not shown) the operation of which is to be timed. The other terminal of 181 is connected to the cathode 13. The secondary 182 is connected across a filament 21 for heating the cathode; one terminal is connected to the cathode.

The apparatus shown in the drawing also includes a relay ICR the coil of which is adapted to be connected across secondary 181 through a starting switch SS. The relay 1RS has a normally closed and a normallyopen contact 23 and 25 respectively.

The apparatus also includes a time-constant network N having a capacitor 31 and a fixed resistor 33 and variable resistor 35 for discharging the capacitor 31. The capacitor 31 of the network is connected in a series circuit extending from the terminal of the secondary 1S1 connected to the anode 11 through a rectifier 37, the normally closed contact 23 of relay 1CR, the capacitor 31 to the terminal of the secondary 182 which is not connected to .the cathode 13 and then the secondary 182 to the other terminal of the secondary 181. The secondary 1S2. is connected in this circuit in such a sense as to oppose the secondary 181 but the potential of the secondary 181 is substantially higher than that of the secondary 182 so that the capacitor 31 may be charged in this circuit with its plate nearer the anode 11 positive and the other plate negative. The fixed and variable resistors 33 and 35 of network are adapted to be connected to the first control electrode 15 through the normally open contact 25 of the relay 1CR.

The apparatus shown in the drawing also includes a biasing network B consisting of a rectifier 41 and a capacitor 43 connected across secondary 182. The capacitor 43 is charged through the rectifier 41 from the potential available across the secondary 182. The network is con- -nected between the second control electrode 17 and the cathode 13 through a grid resistor 45.

In the standby conduction of the apparatus the capacitor 31 ofthe network N is charged from the secondary 181 through the closed contact 23 of the relay lCR substantially to the peak potential existing between the ter- ,minals of the secondary 181. At this time the first control electrode 15 is disconnected from the cathode 11 but the device is maintained non-conducting by the bias impressed 'from the biasing network B between the second control Qatar-s1 electrode 17 and the cathode 11. Since the discharge device lTU is at this time non-conducing, the relay ZCR is deenergized and the controlled apparatus is not in operation. In the use of the apparatus, the starting switch SS is closed actuating the relay 10K. The normally closed contact, of this relay isv then opened interrupting the charging of. the capacitor 31. The normally open contact 25. is closed connectingthe capacitor 31 in a discharging circuit including the fiXed and variable resistors 33 and 37, the control electrode 15, the cathode 11 and the sec{ ondary 182. The capacitor 31 is so connected thatit's positively charged plate is electrically nearerthe electrode 15 and its negatively charged plate is electrically nearer the cathode 11. The discharge device is then rendered conducting actuating relay ZCR and starting operation of the controlled system. I The capacitor now discharges through the fiXed and variable resistors 33 and 35 and the control electrode 15,,and ,th e cathode 1 1. The discharge continues for the duration set by the variable resistor 35 and the time of discharge ,maybe as long as 10 seconds. At the end of the interval the potential supplied by the secondary 1S2 predominates and the charge on thecapacitor 31 is reversed so that the plate nearer to the control electrode 15 becomes negative and the other plate positive. This reversal of, the potential positively renders the discharge deyicenon-conducting. The relay 2CR is then deenergized and stops the operation of the controlled system. ,An interval of the desired duration has thus been timed Since the discharg e device is conducting during the timing of the interval the apparatus is fail-safe. I ,While apreferred embodiment of this invention has been disclosed herein, it isrealizcd that many modificationsthereof are feasible. This invention, then, is not to bevrestricted except insofar as is necessitated by the 'spirit ofthe prior art. I

I claim as my invention; I I I I I 1. In combination, an electric discharge device of the gaseous type having an anode, a cathode and a control electrode, conductors for supplying an alternating potential, a capacitor, rectifier means, selectively actuable switch ,nleansmeans connecting said conductors to said anode and cathode to supply. said alternating potential between said anode and cathode, means connecting said capacitor infa charging circuit with said conductors, said rectifier means and said switch means, said rectifier means I being poled sothat the plate of said capacitor whichjis vcharged negatively is electrically nearer said cathode and the plateof said capacitor which -is chargedrpositivjelyis electrically nearer saidanode, dischargeirnpedanee means forsaid capacitor connected to said control electrod'e,an d means connectedtosaid switch means and responsive to ,actuatio'niof said switch means for opening said charging circuit and connecting said plate of said capacitor which is charged positively to said impedance means whereby said capacitor is discharged through said impedance means and said control electrode and cathode in series. a

2., In combination, an electric discharge deviceof the aseous type having an anode, a cathode and'a control electrode, selec tively actuable normally closed switch means to be opened on actuation of said means, selectively ,actuable normally open switch means to be closed on actuation of said last-named means, rectifier means, capacitor means having a first terminal and a second terminal, conductors for supplying an alternating potential, at chargi 'ng circuit for said capacitor means includingsaid. rectifier means, saidnormally closed switch means and said conductors, said rectifier means being poled so that sfai'd capacitor means is charged with its first terminal positive and its second terminalnegative, means connecting's'aid anode and cathode to said conductors, with said anode e c tricall y nearer said first terminal and said cathode electrically nearer said second terminal to impress "a'n alternating potential between said anode and cathode, a

discharge network for said capacitor including in series impedance means, said control electrode and said cathode,

and means including said normally open switch means for 5 connecting said discharge network across said capacitor with said first terminal electrically nearer said control electrode and said second terminal electrically nearer said cathode.

3. In combination, capacitive means having a first terminal and a second terminal, conductors for supplying a potential, a charging circuit for said capacitive means connected to said conductors for charging said capacitive means so that said first terminal is positive and said second terminal fiegative, an electric discharge device having an anode, a cathode and a control elect-rode, impedance means, a discharging circuit for said capacitive means including in series said impedanceimeans, said control j 'lectro'de and said cathode, said first terminal I lYhear'er said control electrode and said second terminal electrically nearer said cathode insaid I ge cir 'c uit, the instantaneous potential between said 'c'ontrol electrode and cathode being a substantial prop'ortion the instantaneous potent-i al across said capacitor when "said discharging circuit is closed, where'- by said device is conducting so long as said discharging circuit is closed and the potential on said capacitor is above a predeterminedmagnitude, said charging circuit being closed and said discharging circuit being open in the standby conditionofrsaid combination, means connecting'said 'anode and cathode to said "conductors, and selectively actuable means when actuated for opening said charging circuit and closing said discharging circuit.

4 In combine on, capacitive means having a first I nail and a second terminal, first conductors for sup- 3!! pl rig first pio'tenti'al, second conductors for supplying a 6nd potential, means 'for impressing a biasing potential, an electric discharge device having an anode, a cathode, a first control electrode and a. second control electrode, a charging circuit for said capacitive rneansincluding said first conductors for charging said capacitive means with said first terminal positive and said second terminal negative, impedance means, a discharging and recharging circuit for said capacitive "means including said second conductors said impedance means, said firstcontrol electrode and said cathode, said capacijt'ive *rn'eafisjbeing connected in said last-named circuit with saidfir'st terminal electrically nearer said first contr 'e'le trode and said second terminal electrically cathode, fsaid capaeitive means being re I d n sai d l 'aStname'd eireuit with said first terminal and said second terminal positive, means cons cond control electrode and said cathode't'o d pressing means {so that said biasing potential is nnp ssedas 5 a conduction blocking bias between said "I I d control electrode and said cathode, "and means con ct d -to *s'aid circuits and selectively operable for I II ning said -charging circuit closed and said discharging'and ana in circuit open or for maintaining s'aid charging circuit open and said recharging and disclosed.

I 5,5111ebmbinatidn,afirsrconduetor and asecond "conductor tor sii'pp'lying afirst alfernating potential, an -"elech discharge devise having an anode "a cathode, a first "control felecti'ode, and "a second control electrode, n 5 th-ird conductor and a fourth conductor for supplying "a c'ond alternating potential of substantially smaller "amplitude than said first p'ot'ential the potential of said fourth conductor relative to said t-hird conductor being in sppositef hase o ui gpotemial or said second contor relative to; said first'-conductor, means connecting "said first 'conductor to said "anode, "means connecting said second'contactor to said cathode, means connecting said thir d du tor 'to s'aid cathode, i'irst capacitive means'havin ga firstterniinal anda'secdnd terminal, first 7 rectifier means, a charging circuit for "said capacitive fileans including in series ,said .fif'st conductor, said fourth conductor, said third conductor, said second conductor, and said rectifier means, said capacitive means being charged in said circuit so that said first terminal is positive and said second terminal is negative, impedance means, a discharging and recharging circuit for said capacitive means including said impedance means, said first control electrode, said cathode, said fourth conductor "and said third conductor, said capacitive means being means, and said second capacitive means, said second capacitive means being charged in said last-named circuit with said third terminal positive and fourth terminal negative and said third terminal electrically nearer said cathode than said fourth terminal, means connecting said fourth terminal to said second control electrode, and means selectively operable for maintaining closed said charging circuit for said first capacitive means and main- .taining open said discharging and recharging circuit or for maintaining open said last-named charging circuit and maintaining closed said discharging and recharging circuit.

6. The method of timing an operation with an electric discharge device having an anode, a cathode and a control electrode and with a capacitor and a timing 1mpedance, the said method comprising charging said ca- 5 pacitor to a first predetermined potential, impressing the potential across said capacitor, through said impedance, between said control electrode and cathode with said control electrode positive and said cathode negative so that the instantaneous potential between said control electrode and cathode is a substantial proportion of the instantaneous potential of said capacitor, whereby said device is rendered conducting and simultaneously said capacitor is discharged through said impedance and said control electrode and cathode in series at a rate determined by said impedance, and terminating the conduction of said device after said capacitor has discharged to a second predetermined potential lower than said first potential.

7. In combination, an electric discharge device having an anode, a cathode and a control electrode, a time constant network, means connected to said anode and cathode for impressing potential therebetween, means connected to said network for charging said network independently of said control-electrode and cathode, and means connected to said network and to said control electrode and cathode for discharging said network by conduction between said control electrode and said cathode, said network maintaining the control-electrodecathode potential such that the said device is conducting while said network is being discharged and becomes nonconducting after said network is substantially discharged, said discharging means including means for impressing an alternating potential in series with said network, the amplitude of said alternating potential being such that said alternating potential is ineffective until said network is substantially discharged and becomes effective to render said device positively non-conducting when said network is substantially discharged.

8. In combination, an electric discharge device having an anode, a cathode and a control electrode, conductors connected to said cathode for impressing an alternatingcurrent heating potential thereon, a time constant network, means connected to said anode and cathode for impressing potential therebetween, means connected to said network for charging said network independently of said control-electrode and cathode, and means connected to said network and to said control electrode and cathode and including said conductors for discharging said network by conduction between said control electrode and said cathode, said network maintaining the control-electrode-cathode potential such that the said device is conducting while said network is being discharged and becomes non-conducting after said network is substantially discharged.

9. In combination, an electric discharge device having an anode, a cathode, a first control electrode and a second control electrode, conductors connected to said cathode for impressing an alternating-current heating poand to said first control electrode and cathode and including said conductors for discharging said network by conduction between said control electrode and said cathode, said network maintaining the control-elcctrode-cathode potential such that the said device is conducting while said network is being discharged andbecomes non-conducting after said network is substantially discharged, and'means including said conductors and connected to said second control electrode for maintaining said device non-conducting in the standby condition of said combination.

10. In combination, an electric discharge device of the gaseous type having an anode, a cathode and a control electrode, conductors for supplying an alternating potential, a capacitor, rectifier means, selectively actuable switch means, means connecting said conductors to said anode and cathode to supply said alternating potential between saidanode and cathode, means connecting said capacitor in a charging circuit with said conductors, said rectifier means and said switch means, to charge said capacitor to a potential substantially equal to the amplitude of said alternating potential said rectifier means being poled so that the plate of said capacitor which is charged negatively is electrically nearer said cathode and the plate of said capacitor which is charged positively is electrically nearer said anode, discharge impedance means for said capacitor connected to said control electrode, and means connected to said switch means and responsive to actuation of said switch means for opening said charging circuit and connecting said plate of said capacitor which is charged positively to said impedance means whereby said capacitor is discharged through said impedance means and said control electrode and cathode in series.

11. In combination, an electric discharge device of the gaseous type having an anode, a cathode and a control electrode, conductors for supplying an alternating potential, a capacitor, rectifier means, selectively actuable switch means, means connecting said conductors to said anode and cathode to supply said alternating potential between said anode and cathode, means connecting said capacitor in a charging circuit with said conductors, said rectifier means and said switch means, said rectifier means being poled so that the plate of said capacitor which is charged negatively is electrically nearer said cathode and the plate of said capacitor which is charged positively is electrically nearer said anode, discharge impedance means for said capacitor connected to said control electrode, and means connected to said switch means and responsive to actuation of said switch means for opening said charging circuit and connecting said plate of said capacitor which is charged positively to said impedance means whereby a substantial proportion of the potential across said capacitor is immediately impressed through said impedance means between said control electrode and cathode and said device is immediate- 1y rendered conducting and remains conducting while said capacitor is discharged through said impedance ing said capacitor in a charging circuit With said conductors, said rectifier means and said switch means, to

charge said capacitor to a potential substantially equal to the amplitude of said "alternating potential, said recti- -fier means being poled so that the plate of said capacitor whic'h is charged negatively is electrically nearer said cathode and the plate of said capacitor which is charged positively is electrically nearer said anode, discharge impedance means "for said capacitor connected tosaid control electrode, andmeans connected to said switch means and responsive to actuation of said switch means for opening said charging circuit and connecting said plate of said capacitor which is charged positively to said impedance means whereby a substantial proportion of the potential across said capacitor is immediately impressed through said impedahce means between said control electrode and cathode and said device is immediately rendered conducting and remains conducting while said capacitor 'is discharged through said impedance means and said control electrode and cathode in series.

13. In combination an "electric discharge device havfing an anode, a cathode and a control electrode, means connected 'to said "anode and cathode tor impressing thcrebetween a potential such as to maintain said device conducting when the potential between said control elec- "trode and cathode exceeds a predetermined magnitude,

a capacitor, meansconnected to said capacitor for chargling said capacitor to a potential greater than said magniwith the plate of said capacitor that is charged electrically positive electrically nearer said control electrode and the plate of said capacitor charged electrically negative electrically 'nearersaid cathode, the capacity in said network between said control electrode and cathode being small compared to the capacity of said capacitor, whereby when said capacitor is charged by said charging rhea'r'is as aforesaid, said device is rendered conducting when said capacitor is connected in said network and remains conducting until said capacitor discharges to a potential lower than said predetermined potential.

14 The method of timing and operating with an electric discharge device having an anode, a cathode and a control electrode and with a capacitor and a timing impedance, the said method comprising charging said capacitor to a first predetermined potential, impressing the potential across "said capacitor, through said impedance, between said control electrode and cathode with said control electrode positive relative to 'said cathode so'that the instantaneous potential between said control electrode and cathode is a substantial proportion of the instantaneous potential of said capacitor, whereby said device is rendered conducting and simultaneously said capacito'r is discharged through said impedance and said control electrode and cathode, ata rate determined by said impedance, and superimposing in the circuit of said capacitor, impedance and control electrode and cathode an alternating potential of a predetermined magnitude to terminate thelco'nduction of said device after said capacitor has discharged to a second predetermined potential lower than said first potential.

References Citedin the file of this patent UNITED STATES PATENTS 1,980,146 Vingerhoets Nov. 6,1934 2,132,264 King Oct. 4, 1938 r 2,133,670 Schuchmann Oct. 18, 1938 2,404,553 Wales July 23, 1946 2,487,150 Lexa Nov. 8, 1949 2,607,907 Marshall Aug. 19, 1952 2,641,701 Moore June 9, 1953 

